Device for cooling surface that rotates about a rotation axis and that faces the rotation axis

ABSTRACT

A device ( 4 ) comprises a container ( 40 ) for a liquid coolant ( 41 ) that is disposed between the axis ( 1 ) and the surface ( 30 ) facing the axis to co-rotate with the surface. The device is further provided with an atomizer nozzle ( 42 ) of the container, facing the surface, from which the coolant is discharged during rotation of the container due to the centrifugal force (F) acting upon the coolant of the container in the form of an atomized jet ( 43 ) that strikes the surface. The device cools a surface of an electronic device ( 3 ) that runs hot, the electronic device supplying the X-ray source of a computer tomograph with power and rotating about the axis of the gantry ( 2 ) of the tomograph.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the 35 USC 371 national stage of internationalapplication PCT/DE01/03641 filed on Sep. 20, 2001, which designated theUSA.

FIELD OF THE INVENTION

The invention relates to a device for cooling a surface that rotatesabout a rotation axis and that faces the rotation axis.

BACKGROUND OF THE INVENTION

An example of a surface to be cooled that rotates about a rotation axisand that faces the rotation axis is a surface of an electronic devicethat becomes hot, said electronic device supplying electrical power tothe X-ray source of a computer tomograph and rotating together with theX-ray source about a tube designed to accommodate a patient to beexamined. Such a system is also known as a “gantry”.

With a computer tomograph of this type, it is desirable to achieve thehighest possible rotational frequency, since on the one hand thisenables the number of tomography examinations performed per time unit tobe increased and on the other images of fast-moving organs (e.g. theheart) are possible free of artifacts.

The limiting variable for the maximum achievable rotational frequency isthe total mass that is to be brought into rotation, which includes,inter alia, not only the X-ray detector but also the mass of the X-raysource, the mass of the device for supplying electrical power to theX-ray source and the mass of a device co-rotating with the X-ray sourceand serving to cool a surface of the device for supplying the electricalpower, said surface becoming hot. The smaller this total mass is, thegreater is the maximum achievable rotational frequency. At the same timethe rotation radius can be reduced by reducing the size of components,resulting in an overall reduction in the centrifugal force.

A reduction of each individual mass contributing to the total mass initself causes a reduction in the total mass, as does a reduction in themass of the device for cooling a surface of the device that becomes hot,said device supplying electrical power to the X-ray source.

SUMMARY OF THE INVENTION

The invention specified in claim 1 advantageously provides a device forcooling a surface that rotates about an axis and that faces the axis,said device co-rotating with the surface and exhibiting a low-massdesign.

The device according to the invention mainly comprises a container for aliquid coolant that is disposed between the axis and the surface to becooled facing said axis to co-rotate with the surface, and at least oneatomizer nozzle of the container that is turned toward the surface andfrom which the coolant is discharged during rotation of the containerdue to the centrifugal acting upon the coolant in the container in theform of an atomized jet that strikes the surface.

The device according to the invention cleverly uses the rotation toapply an efficient atomization cooling technique. In particular, thehighly efficient and known technique of “spray cooling” with all itsadvantages can be employed, the centrifugal force advantageously beingused as a “compressor”. The centrifugal force acts on the coolant in therotating container and generates a sufficiently high pressure which isenough to spray the coolant through the atomizer nozzle onto the surfaceto be cooled.

The device according to the invention is advantageously suitable forgeneral use wherever a surface that rotates about an axis and that facesthe axis is to be cooled, and at the same time, on account of its lowmass, advantageously permits a high maximum achievable rotationalfrequency and/or an increase in the rotational frequency compared to theprior art owing to the reduction in centrifugal force.

An advantageous embodiment of the device according to the invention isimplemented or could be implemented such that the atomized jet strikesthe surface to be cooled obliquely at an angle rather than vertically.This can preserve/achieve an optimal homogeneity of the coolant sprayedonto the surface to be cooled and consequently an improved coolingeffect.

In an advantageous development of this embodiment, the angle at whichthe atomized jet obliquely strikes the surface to be cooled can be setas a function of the rotational frequency of this surface.

An atomized jet obliquely striking the surface to be cooled at an angleis produced, for example, if the atomized jet is discharged from theatomizer nozzle using a spray axis that is aligned vertically relativeto the surface. The atomized jet is deflected on its way from the nozzleto the surface to be cooled due to the effect of the Coriolis force inthe plane of rotation and strikes the surface obliquely at an angle. Thesize of this angle depends on the rotational frequency and is all thegreater, the greater the rotational frequency.

Notwithstanding this, an atomized jet striking the surface to be cooledobliquely at an angle can be produced in that the atomized jet isdischarged from the atomizer nozzle with a spray axis aimed at such anoblique angle to the surface to be cooled that the atomized jet strikesthe surface obliquely at an angle. In this case the angle at which theatomized jet obliquely strikes the surface to be cooled can, forexample, be set by the angle of the spray axis relative to this surface.The last-mentioned angle can be set as a function of the rotationalfrequency of the surface.

An advantageous development of the device according to the inventionfeatures a closed-loop coolant device in which the atomized coolant inwhich the atomized coolant is collected after striking the surface to becooled and channeled back to the container.

In a preferred and advantageous embodiment of this development, theclosed-loop coolant device features a cooling surface on which coolantthat has vaporized on the surface to be cooled condenses.

In a particularly preferred and advantageous embodiment of the deviceaccording to the invention, the surface to be cooled is a surface of anelectronic device that becomes hot, said device rotating about a tubedesigned to accommodate a patient to be examined and serving to supplyelectrical power to the X-ray source of a computer tomograph.

As a further application it is also conceivable to use such a coolingdevice for cooling the target, i.e. the anode of the X-ray sourceitself, in a similar manner. Accordingly, an advantageous embodiment ofthe device according to the invention is implemented such that thesurface to be cooled is a surface of a target that becomes hot, saidtarget being that of an X-ray source of a computer tomograph rotatingabout a tube designed to accommodate a patient to be examined.

Advantages of each of these last-mentioned devices are:

-   -   the device can dissipate heat highly efficiently from the        surface to be cooled of the device serving to supply electrical        power to the X-ray source and/or the X-ray source itself;    -   its low mass reduces the total mass of the tomograph to be set        into rotation (rotating part of the gantry) and permits a        desired higher maximum achievable rotational frequency, which        increases the efficiency of the tomograph by increasing the        tomography examinations that can be performed per time unit        and/or enables images of fast-moving organs to be generated free        of artifacts;    -   it requires only that the device for supplying electrical power        to the X-ray source is disposed such that its surface to be        cooled is turned toward the rotation axis;    -   it permits the device for supplying electrical power to the        X-ray source to be built using power electronics components,        thereby once again reducing the total mass of the tomograph that        is to be set into rotation and once again increasing the maximum        achievable rotational frequency, with the result that the size        of the rotating part of the tomograph and the rotation radius        are considerably reduced.

BRIEF DESCRIPTION OF THE DRAWING

The invention is explained in greater detail in the followingdescription with the aid of the drawings provided by way of example:

FIG. 1 shows a schematic representation of an embodiment of a deviceaccording to the invention for cooling a surface of the gantry thatbecomes hot and that is mounted on the rotating part of the gantry andco-rotates with this part,

FIG. 2 shows a schematic representation showing the atomized jetdischarged from an atomizer nozzle of the embodiment of the deviceaccording to the invention with a spray axis that is vertical relativeto the surface to be cooled, said jet striking the surface obliquely atan angle due to the Coriolis force acting upon it, and

FIG. 3 shows a schematic representation showing the atomized jetdischarged from an atomizer nozzle of the embodiment of the deviceaccording to the invention with a spray axis aligned obliquely at anangle to the surface to be cooled, said jet striking the surfaceobliquely at an angle.

The figures are not to scale.

DETAILED DESCRIPTION OF THE INVENTION

The part of the gantry of an exemplary computer tomograph shown in FIG.1 has an axis 1 which is positioned vertically relative to the drawingplane of FIG. 1 and about which the rotating part of the gantry of thetomograph revolves.

Axis 1 is at the same time a longitudinal axis of the merely indicatedstationary tube 2 of the gantry, said tube serving to accommodate apatient. The accommodated patient is moved in the interior 20 of thetube 2 along the axis 1 which is also contained in the interior 20.

The part of the gantry of the tomograph rotating about the axis 1 andthe tube 2 comprises, inter alia, an X-ray source, the X-ray detector,an electronic device for supplying electrical power to the X-ray sourceand a device for cooling a surface to be cooled of a device of therotating part of the gantry, said device becoming hot. The device thatbecomes hot is represented symbolically in FIG. 1 by a box identified by3. It is mounted on the rotating part of the gantry and co-rotates insynchronism with this part about the axis 1 and the tube 2, for examplein the direction of the arrow 10.

The device 3 that becomes hot is, for example, the device for supplyingelectrical power to the X-ray source, preferably built usingsemiconductor components, the surface to be cooled being a surface ofthis device that becomes hot and that faces the axis 1, and/or the X-raysource itself, the surface to be cooled being a surface of the anode ofthis source that becomes hot and being turned toward the axis 1, saidsurface preferably being a backside surface of the grounded anode.

The surface to be cooled of the device 3 is symbolically represented inFIG. 1 by the side surface of the box identified by 30 that is turnedtoward the axis 1. The surface to be cooled 30 is, for example,positioned vertically relative to the drawing plane of FIG. 1.

The device for cooling the surface to be cooled 30 is identified by 4and is disposed between the tube 2 and the surface to be cooled 30 ofthe device 3.

According to the invention, the device 4 for cooling the surface 30 ofthe device 3 comprises a container 40 for a liquid coolant 41 that isdisposed between the tube 2 and the surface 30 of the device 3 toco-rotate with the device 3 and the surface 30, and at least oneatomizer nozzle 42 of the container 40 that is turned toward the surface30 and from which the coolant 41 is discharged during rotation of thecontainer 40 in the form of an atomized jet 43 due to the centrifugalforce F acting upon the coolant 41 in the container 40, said atomizedjet 43 striking the surface 30 of the device 3.

Since the container 40 is disposed between the tube 2 and the surface 30of the device 3 and the axis 1 is located in the interior 20 of the tube2, the container 40 is necessarily disposed between the axis 1 and thesurface to be cooled 30 that is turned toward this axis, which,ultimately, is what matters.

The co-rotation of the container 40 with the device 3 and the surface 30means that the container 40 rotates about the axis 1 in synchronism withthe device 3 and the surface 30 in the direction of the arrow 10, forexample owing to the fact that the container 40 and the device 3 arepermanently joined to each other.

The centrifugal force F generated during the rotation of the container40 about the axis 1 and acting upon the coolant 41 in the container 40acts radially in the direction away from the axis 1, i.e. in thedirection of the arrow 11. The amount of the centrifugal force F isgiven by the equation |F|=m·r·ω², where m stands for the mass of thecoolant 41, r for the radial distance of the coolant 41 from the axis 1during the rotation, and ω for the angle speed of the rotation.

The centrifugal force F acting vertically upon the surface 410 that isturned toward axis 1 of the liquid coolant 41 in the container 40generates a hydrostatic pressure in the coolant 41 that causes thecoolant 41 to be discharged from the atomizer nozzle 42 in the form ofthe atomized jet 43, by means of which the coolant 41 is sprayed ontothe surface to be cooled 30 of the device 3 in the form of small coolantparticles.

Owing to the rotation it is known that the Coriolis force acts upon eachcoolant particle of the atomized jet 43 moving from the atomizer nozzle42 toward the surface 30, said force being directed in the oppositedirection to the arrow 10 and deflecting the coolant particle in thisopposite direction. This causes the atomized jet 43, or more accuratelya spray axis of the atomized jet 43, to be deflected en route betweenthe atomizer nozzle 42 and the surface to be cooled 30.

This is shown in slightly exaggerated form in FIG. 2. It is assumed, forexample, that the atomized jet 43 is discharged from the atomizer nozzle42 with a spray axis 430 aligned vertically relative to the surface tobe cooled 30. This is indicated in FIG. 2 by the fact that in the areaof the atomizer nozzle the spray axis 430, represented by a dash-dottedline, is vertical with respect to a conceptual surface 30′ representedby a dashed line and running parallel to the surface to be cooled 30 andpositioned vertically relative to the drawing plane of FIG. 2.

A coolant particle 431 being discharged from the atomizer nozzle 42 andmoving along the spray axis 430 does not continue in a straight line enroute to the surface 30, but is deflected due to the Coriolis forceF_(c) acting in the direction of the arrow 10′ contradirectionally tothe arrow 10 and moves on a path deflected to the left in FIG. 2, whichdefines the now deflected spray axis or spray trajectory 430 of theatomized jet 43.

Similarly, coolant particles 431 of the atomized jet 43 (?) not locatedon the spray axis 430 move laterally with respect to the spray axis 430on deflected paths relative to the surface 30, as indicated by dashedlines 430′. Thus, the atomized jet 43 is deflected overall and strikesthis surface 30 obliquely at an angle. This angle is represented in FIG.2 by the angle α<90° between the spray axis 430 striking the surface 30and this surface 30.

If the atomized jet 43 strikes the surface 30 at an oblique angle, thisfavors the attainment of an optimal homogeneity of the coolant 41sprayed onto the surface 30, since the impetus transmitted each time tothe surface 30 from the moving coolant particles 431 is not directedprecisely radially, but also has a component parallel to the surface 30which encourages the sprayed-on coolant to flow in the direction of thiscomponent.

The angle α depends on the angle speed ω of the rotation and thereforeon the rotational frequency. If this is unsuitable for achieving asufficiently small angle α<90°, a way to assist is by causing theatomized jet 43 to discharge from the atomizer nozzle 42 with a sprayaxis 430 aligned obliquely at an angle relative to the surface to becooled 30.

A case of this type is shown in FIG. 3. FIG. 3 differs from FIG. 2 onlyin that the spray axis 430 is tilted in the area of the atomizer nozzle42 contradirectionally to the direction of rotation 10 obliquely at anangle β<90° to the left with respect to the level 30. The smaller theangle β is chosen, the smaller is the angle α.

In this case the angle α can be set as a function of the rotationalfrequency by setting the angle β, particularly to a value that is alwaysoptimal for cooling the surface 30.

Instead of only one atomizer nozzle 42, two or a plurality of atomizernozzles 42 can be present, their atomized jets 43 particularly strikingthe surface 30 obliquely from different directions.

The surface to be cooled 30 can, for example, also be disposed obliquelyrelative to a radially aligned atomizer nozzle 42 and furthermore doesnot have to be level, but can be bent into a convex and/or concaveshape.

The device 4 shown in FIG. 1 for cooling the surface 30 of the device 3exhibits a closed-loop coolant device 5 in which the atomized coolant 41is collected after striking the surface to be cooled 30 and returned tothe container 40. In particular, this closed-loop device 5 exhibits acooling surface 50 on which coolant 41 which has vaporized on thesurface to be cooled 30 condenses.

The device operates, for example, as follows: The coolant 41 constantlysprayed onto the surface to be cooled 30 forms a coolant film 411 onthis surface 30, from which coolant 41 constantly vaporizes; saidcoolant film 411 being indicated by a dashed line.

Due to the centrifugal force F, the resulting coolant vapor 412indicated by dashed arrows moves radially away from the axis 1, asindicated by the deflection of the dashed arrows, and reaches aco-rotating wall 6 which closes off the rotating parts of the tomographradially toward the outside and is preferably bent around the axis 1,said wall for example being cooled by a self-generating airstreamproduced during the rotation.

The surface of the wall that is turned toward the axis 1 forms thecooling surface 50, which is reached by the coolant vapor 412 and onwhich the coolant vapor 412 is deposited as a coolant condensate whichforms a coolant film 413 that is spread evenly over the entire coolingsurface 50, said film being pressed against the cooling surface 50 bythe centrifugal force F.

If the rotational frequency were to be stepped down, the coolant 41contained in the coolant film 413 could automatically flow away, forexample via side walls 7, in the direction of axis 1, collected incollecting funnels 8 and returned by the collecting funnels 8 to thecontainer 40.

The collected coolant 41 can be returned if necessary, e.g. duringconstant rotation of the gantry, with the aid of pumps 9. However, suchpumps 9 complicate the design of the device 4 and increase the mass tobe set into rotation.

An inert coolant that does not react chemically with the parts withwhich it comes into contact is preferably used as coolant 41. Fluorinertcan be used, for example.

In the prior art, the device 3 for supplying electrical power to theX-ray source of the tomograph is constructed using standard componentsand power electronics modules that are relatively heavy and have a lowratio of chip to package mass.

Cooling is effected by means of active air or water cooling, the watercooling solution operating more effectively but also implying a highertechnical overhead and being associated with larger masses. However, aircooling also means considerable volume, and therefore weight, as aresult of the necessary heat storage capacity of the heatsink.

In the case of the novel tomograph equipped with the device 4 accordingto the invention for cooling the surface 30 of the device 3, there isthe additional possibility that the device 3 advantageously features notthe relatively heavy cooling components and modules exhibiting a lowratio of chip to package mass, but power electronics components oflightweight design, thereby once again reducing the tomograph mass thatis to be set into rotation and further simplifying the design of therotating part of the tomograph.

The device according to the invention for cooling a surface that rotatesabout a rotation axis and that faces the rotation axis is not limited tothe application in a tomograph.

1. Device (4) for cooling a surface (30) that rotates about an axis (1) and that faces the axis (1), which comprises a container (40) for a liquid coolant (41) that is disposed between the rotation axis (1) and the surface (30) for a co-rotation with the surface (30), and at least one atomizer nozzle (42) of the container (40) which faces the surface (30) and from which the coolant (41) is discharged during rotation of the container (40) due to the centrifugal force (F) acting upon the coolant (41) in the container (40) in the form of an atomized jet (43) that strikes the surface (30).
 2. Device according to claim 1, the atomized jet (43) striking the surface to be cooled (30) obliquely at an angle (α).
 3. Device according to claim 2, the angle (α) at which the atomized jet (43) obliquely strikes the surface to be cooled (30) being selectable as a function of the rotational frequency of this surface (30).
 4. Device according to claim 1, comprising a closed-loop coolant device (5) in which vaporized coolant (41) is collected after striking the surface to be cooled (30) and returned to the container (40).
 5. Device according to claim 4, the closed-loop coolant device (5) featuring a cooling surface (50) on which coolant (412) which has vaporized on the surface to be cooled (30) condenses.
 6. Device according to claim 1, the surface to be cooled (30) being a surface that becomes hot of an electronic device for supplying electrical power to an X-ray source of a computer tomograph, said electronic device rotating about a tube (2) for accommodating a patient to be examined.
 7. Device according to claim 1, the surface to be cooled (30) being a surface that becomes hot of a target of an X-ray source of a computer tomograph rotating about a tube designed to accommodate a patient to be examined. 